Method and apparatus for continuous liquid thermal diffusion



May 13, 1958' A. 1-. FELLOWS ETAL ,8

METHOD AND APPARATUS FOR commuous LIQUID THERMAL DIFFUSION Filed Aug. 25. 1954 2 Shets-Sheet 1 INVENTORS BY Janus jghfg a ATT gaN EY y 958 A. T. FELLOWS ETAL 2,834,464

METHOD AND APPARATUS FQR CONTINUOUS LIQUID THERMAL DIFFUSION Filed Aug. 23. 1954 2 Sheets-Sheet 2 I 2a I Z4 I I 30' z? {I ATToNEY United States Patent() M lVIETHOD AND APPARATUS FOR CONTINUOUS LIQUID THERMAL DIFFUSION,

Albert T. Fellows, Woodhury Heights, and James R.

White, Wenonah, N. J., assignors to Socony Mobil Oil Company, Inc., a corporation of New York This invention relates to an improved method and apparatus for eifecting continuous liquid thermal diffusion. More particularly, the present invention is directed to a method and apparatus for continuously and uniformly charging a liquid feed containing two or more unlike components to a thermal diffusion zone and continuously and uniformly Withdrawing separated or purified components from said zone. More specifically, the instant invention is concerned with an apparatus and method wherein continuous uniform lateral distribution of a liquid feed and resulting separated finished products is achieved over the working surface in a thermal diffusion column.

It has heretofore been known to employ thermal diffusion as a means for separating fluids containing two or more unlike components. Thus, when a fluid mixture is subjected to a temperature differential, the mixture undergoes changes in composition at the places of different temperature by reason of thermal diffusion and it has been proposed to utilize such phenomena to separate fluid mixtures into a fraction enriched in one component of the mixture on the one hand and a fraction substantially depleted of said component on the other hand.

Thermal diffusion has been employed for separating both gaseous and liquid mixtures of dissimilar components. In separation of mixtures by thermal diffusion, it has been observed that there is a wide difference in the results obtained, depending upon whether gaseous or liquid thermal diffusion is being efiected. While there are relatively satisfactory theories of thermal diffusion in the gaseous state, those theories which have been brought forward for explanation of thermal diffusion in the liquid state all fail in important respects. Liquid thermal diffusion accordingly involves diiferentor additional determining factors not found in gaseous thermal diffusion. Consequently, predictions with regard to liquid thermal diffusion cannot be predicated on conclusions drawn with reference to gaseous thermal difius'ion. The apparatus and process with which .the instant invention is concerned specifically relate to thermal diffusion in the liquid state.

It has been postulated that in liquid thermal diffusion the molecules of certain materials or components acquire greater kinetic energy by absorption .of 'heat from the hot wall than do the molecules of the other material or component and that, as a result, .those molecules acquiring the higher kinetic energy will tend to move away from the hot Wall, and this motion may be favored or hindered according to the shape or compactness of the molecules comprising the mixture. In any event, a convection current is set up in the slit defined by the hot and cold walls so that the liquid adjacent the hot wall Patented May 13, 1958 other components will rise adjacent the hot wall in the slit and flow into the upper part of the slit. Liquid thermal difiusion has been carried out both as a batch type process and as a continuous operation. In effecting thermal diffusion on a batch basis, the thermal diffusion column, consisting essentially of a narrow and elongated slit in a non-horizontal position, has been filled with a liquid containing unlike components and a temperature gradient has been maintained between opposite walls of the slit for an extended period of time, after which one end of the slit has been found to contain a higher concentration of one of the unlike materials than the other end. Continuous thermal diffusion has been carried out by continuously introducing the liquid containing unlike components into a narrow slit formed by two surfaces and maintaining a temperature gradient across the slit, continuously withdrawing from one part of the slit a fraction that is richer in one of the unlike components than the initial liquid feed and continuously withdrawing from another part of the slit another fraction which is richer in another of the unlike components than the initial liquid feed.

Thus, thermal diffusion has been employed as a means for separating mixtures containing two or more components which are liquid under the conditions of separation. Mixtures composed of two or more components dissolved in a common solvent, solutions of one component in another, mixtures of .two or more components in the liquid state, etc., have been separated, purified, enriched, and concentrated by thermal dilfusion techniques. Such techniques have been useful in attaining separation of unlike components of liquids and solutions such as in the concentration of vitamins from mixtures of the same with materials having little or no vitamin activity; the separation of petroleum, vegetable, and animal oils into components of differing physical and chemical characteristics; the concentration of antibiotics from solutions of the same; and in the separation and purification of a variety of other liquid materials or materials which maybe placed in the liquid state for purposes of separation and purification. Thermal diffusion has been particula'rly useful in attaining separation of unlike materials having only slight differences, such as azeotropic mixtures, isomers, and isotopes.

The apparatus and methods heretofore employed for effecting liquid thermal dilfusion, both as a batch and continuous operation, have involved the introduction of a liquid stream containing two or more unlike components into a thermal diifusion zone and the maintenance of a temperature gradient across the liquid stream and between the surfaces comprising said zone. Due to the difference in temperature, one component or group of components concentrate in one part of the working zone or slit and a second .component or group of components concentrate in another part of the slit. The components so separated have thereafter been withdrawn from the thermal diffusion zone. In such previous methods and apparatus, entry and withdrawal ports to and from the slit area have been point sources. In batch operation the manner of introduction of the liquid ,stream is not considered to be important, it being only necessary that the slit area be filled with liquid and a temperature gradient thereafter applied to the liquid contained in the slit. in continuous liquid thermal diifusion, however, it has been found that the introduction of the liquid feed as a point source to a thermal diffusion column and the withdrawal of separated products as point sources has resulted in ineflicient operation in that only a portion of the working space has thereby been utilized. Thus, it has been observed that when liquid is added to a thermal diifusion column "working space, the added liquid rises or falls more or less asan entity in the ambient liquid, undergoing very little lateral displacement or fanning out as it moves. With the introduction or discharge of the feed liquid and resulting separated products through essentially point sources relative to the lateral length of the Working space, much of the thermal diffusion column is thus wasted since the same is not being employed for its intended purpose.

The method and apparatus of the present invention afford a more effective and efficient means for carrying out continuous liquid thermal diffusion than has been available in previous operations. In accordance with the instant invention, an apparatus and method are provided wherein the feed liquid is uniformly and laterally distributed over the working surface of the thermal diffusion zone by introducing the same to said zone as a continuous and uniform laterally distributed stream under conditions of uniform pressure. Likewise, the separated finished products are continuously and uniformly withdrawn from the slit or working area under uniform pressure conditions. Means for providing uniform lateral distribution of the feed liquid and uniform lateral withdrawal of the finished separated products are achieved in accordance with the present invention by introducing the feed liquid and withdrawing the finished products through continuous slots extending laterally across the surface defining the thermal diffusion zone.

One embodiment of the invention resides in the provision for effecting uniform lateral distribution through slots extending across the lateral dimension of the surfaces comprising the slit and directly communicating therewith. In such provision, the feed enters a slot and the product streams leave the thermal diffusion zone through other slots, one positioned above and one positioned below the feed slot. Another embodiment for effecting uniform lateral liquid distribution in the thermal diffusion zone is the provision of horizontally elongated slots extending laterally across the surfaces comprising the slit for both the feed and product withdrawal streams, in which said streams are introduced and withdrawn through the numerous and connecting pores of a porous structure of suitable thermal and chemical characteristics. Porous metal structures, such as bronze, stainless steel or porous plastics; porous sintered glass; porous graphite and carbon, are representative of suitable materials for effecting the respective introduction and withdrawal of the liquid feed and product streams. It is to be understood that, in accordance with the instant invention, uniform liquid flow through the slots is essential to attain the desired uniform lateral distribution. The slots either unobstructed, i. e., directly communicating with the slit, or provided with an intermediate porous structure, as aforementioned, communicate with a uniform pressure manifold. The resistance to flow through such slots is uniform over the lateral dimension. embodiments there may be any desired number of product withdrawal streams, each designed for uniform lateral product withdrawal as designated herein.

The word slit as used herein is intended to refer to an extended thin space between a hot surface and a cold surface, in which space the thermal diffusion is accomplished. The word slot as used herein is intended to refer to a horizontal narrow opening in one of the surfaces comprising the slit through which liquid passes to or from said slit.

Having described in a general way the nature of this invention, it may be more readily understood and the advantages thereof apparent from a consideration of the accompanying drawing wherein:

Figure 1 is an elevational view of a plate type thermal diffusion column utilizing the feed and withdrawal system of the invention.

Figure 2 is an elevational view of the inner surface of one of the plates of a thermal diffusion column illustratingthe feed and withdrawal slots.

It is to be understood that in these r Figure 3 is anelevational view of a concentric type thermal diffusion column utilizing the feed and withdrawal system of the invention.

Figure 4 is a detailed view showing one of the slit surfaces provided with an unobstructed slot.

Figure 5 is an end view of the surface shown in Figure 4.

Figure 6 is a detailed view showing one of the slit surfaces provided with a porous feed or withdrawal opening.

Figure 7 is an end view of the surface shown in Figure 6.

Referring more particularly to Figures 1 and 2, the apparatus shown comprises parallel plates 10 and 11 which may be of the same or different materials spaced from one another as by a spacing gasket 12 defining the thickness of the slit and positioned around the periphery of the working space between the plates and if necessary by small spacers of the same thickness at intermediate points within the slit 13 formed by the inner opposed plate walls. Plate 10 is provided at its upper and lower end with withdrawal outlets 14 and 15 and at an intermediate position with feed inlet 16. The feed inlet 16 may be located half-way between withdrawal outlets 14 and 15 or at a point closer 'to one of the withdrawal outlets than to the other and there may be more than one outlet, not shown, above the feed and more than one outlet, not shown, below the feed. Outlets 14 and 15, as well as inlet 16, are shown on plate 10, but it is to be understood that one or more may alternately be placed on plate 11 as experimental convenience and desirability may dictate. Inlet 16 and outlets 14 and 15 comprise elongated horizontally positioned tubes 17 extending laterally in back of the surface of either one or both of the plates defining the slit. Each of the tubes 17 is pierced by a long horizontal continuous slot 18 extending along that portion of the tube length which is in back of the lateral width of the thermal diffusion working space and affording direct communication between slit 13 and the interior of the tubes 17. The continuous introduction of a liquid feed comprising two or more unlike components takes place through feed inlet 16. The liquid feed then passes through tube 17 communicating with inlet 16 and is discharged through slot 18, under conditions of uniform pressure, so as to be laterally and uniformly distributed over the surface of the plates comprising slit 13. One of the plates is maintained at a higher temperature than the other by suitable means to afford a temperature gradient therebetween. Thus, the plates 10 and 11 are respectively provided with jackets 5t) and 51. Jacket 50 is provided with at least a pair of ports 52 and 53. A suitable cooling medium is introduced through port 52 and withdrawn through port 53. Jacket 51 is similarly provided with at least a pair'of ports 54 and 55. A suitable heating medium is introduced through port 54 and withdrawn through port 55. The resultant temperature gradient across slit 13 causes thermal diffusion to take place in the liquid within the slit so that the position of liquid adjacent the hot surface of the slit becomes more concentrated in one of the unlike liquid components and the other portion adjacent the cold surface of the slit becomes more concentrated in another of the unlike components of the initial liquid feed. The portion of the thermally diffused liquid carried upwards by convection is continuously withdrawn laterally and uniformly over the surface thereof through slot 18, communicating with outlet 14. In similar manner, the portion of thermally diffused liquid carried downwards by convection is continuously withdrawn laterally and uniformly over the surface. thereof through slot 18, communicating with outlet 15.

The apparatus illustrated in Figure 3 includes an outer tube 20, the inner surface 21 of which constitutes one wall of a slit 22 and a hollow inner tube 23 arranged concentrically with relation to the outer tube 20, the outer surface 24 of said inner tube 23 constituting the other wall of slit 22. The distance between surface 24 of the inner tube 23 and the surface 21 of the outer tube 20 is maintained substantially uniform by means of spacing rings 25 at or near the ends'of the tubes and, if necessary, by spacers of same thickness at intermediate points within the slit 22. The outer tube 20 is pierced along its circumference near its upper and lower ends and half way between or at some intermediate point by a plurality of slots 26. The slots 26 are of substantially uniform size and each set of the slots extending circumferentially around tube 20 lies in a plane perpendicular to the axis of said tube. Surrounding and enclosing each set of the slots 26 are doughnut-like tubes 27, 28, and 29, the interior of the latter tubes being in direct communication with the underlying slots 26. Tubes 27 and 29 are provided with withdrawal outlets 30 and 31', respectively, and tube 28 is provided with feed inlet 32. It is not essential that the feed inlet 32 be on the same side of the outer tube 20 as the withdrawal outlets 3t and 31 as shown in Figure 3. Inlet 32 and outlets 30 and 31 may, if desired, be on opposite sides of tube 20 or at any feasible angle or angles to one another. Also, it is to be realized that, while for purposes of simplicity in illustration only two outlets have been shown, any desired number of outlets may be employed positioned above and below the feed inlet. The continuous introduction of a liquid feed comprising two or more unlike components is effected through feed inlet 32 and is thereafter conducted through tube 28 and underlying slots 26, being laterally and uniformly distributed over surface 21 of slit 22. one of the slit surfaces is maintained at a higher temperature than the other by suitable means,- not shown, to afford a temperature gradient therebetween. The resultant temperature gradient across slit 22 causes thermal diffusion to occur in the liquid within the slit so thatthe portion of liquid adjacent the hot surface of the slit becomes more concentrated in one of the unlike liquid components and the other portion adjacent the cold surface of the slit becomes more concentrated in another of the unlike components of the initial liquid feed in the same manner as described with reference to Figure 1. The temperature gradient also results in a convection current within slit 22 so that the liquid component adjacent the hot surface rises to the top and the component adjacent the cold surface descends to the bottom of the slit. The component that concentrates adjacent the hot wall of the slit, and therefore rises to the top, is continuously withdrawn laterally and uniformly over the surface of said wall through slot s 26 communicating with tube27 and outlet 30. Likewise, the component that concentrates adjacent the cold surface and descends to the bottom of the slit is continuously withdrawn laterally and uniformly through slots 26 communicating with tube 29 and outlet 31. I

Figures 4 and 5 show in detail a section of a slit wall 40 which may be either plane or curved, provided with a liquid feed 'or withdrawal tube 41 having an elongated slot 42 extending laterally along the surface of wall 40, serving to effect uniform lateral distribution over said surface of liquid flowing through tube 41.

Figures 6 and 7 show in detail a section of a slit wall 43 which may be either plane or curved, provided with a liquid feed or withdrawal tube 44 leading to an elongated chamber 45 extending laterally along the surface of wall 43 and formed of or filled with a suitable porous structure to an extent suflicient to effect uniform lateral distribution over said surface of liquid flowing through tube 44 and thereafter through the aforesaid porous structure.

Uniform lateral distribution of the feed and product streams over the surfaces of the slit in a continuous liquid thermal diffusion column has been found to afford a greatly enhanced efficiency of separation, permitting an appreciably greater liquid throughput rate or the desired degree of separation to be carried out with an unexpected sav- 6 ing in time and energy, as willbe evident from a consideration of the following illustrative example:

In a metal parallel plate apparatus having a slit thickness of 0.03 inch and plates foot wide ancl 2 feet high,

the hot plate being provided with a feed slot near the bottom and a top product slot near the top and the cold plate being provided with a bottom product slot at the bottom, the feed thus being between theproduct outlets, the exact position of the slots not otherwise being critical, good separations were obtained when the full working length of the slots was employed, which was 9 inches due to gasket widths, in both feed and product withdrawal. If the slots were partially blocked off, the degree of separation-was decreased.

An unrefined oil having a viscosity of 190 centistokes at 100 F. was fed into the above-described apparatus operating under the following conditions:

Temperature, cold side 2 .i .;C Temperature, hotside C 1 73 Ratio, vol. top to bottom product 1:1

FULL SLOT USED FOR FEED AND PRODUCTS Viscosity at F., Cs.

Feed Rate Top 1315111. Product Product 4 cc./min 271 8 cc./min 148 252 ONE-THIRD SLOT USED FOR FEED AND PRODUCTS 4 cc. Imin 149 255 S cc./min 163 230 In these experiments the viscosity measures the extent of the separation achieved, or in terms of a useful process, the viscosities are a measure of the quality of the separated streams. Since the heat dissipated in maintaining the temperature gradient was the same in the two groups of experiments, it is apparent that an increase in lateral length of the slots from to full open permitted the same quality streams to be made at double the feed or throughput rate. Or, the same amounts of the same quality of separated streams were made for half the energy expenditure.

After the above experiments were made, the plates were separated and adhering oil was wiped off. The oil was discovered to have stained the plates in a manner that revealed the flow of the oil during the last pair of experiments. The hot plate was stained by oil streamlines in a manner that indicated the region of principal flow. Where the slots were open /3 of length), flow was predominant. Where the slots were closed /3 of length) flow was at a minimum. This stain pattern revealed that uniform lateral distribution must be achieved by arrangements which form the subject of this invention. In the absence of such arrangements, uniform lateral distribution 'was not realized.

. While it is to be understood that it is within the scope of this invention to carry out the desired separation in a horizontal slit and that it is quite'possible to withdraw the unlike fractions therefrom without causing them to intermingle appreciably, it is preferred to operate with a substantially vertical slit for the reason that the "mechanical difliculty of effectively withdrawing the unlike fractions is thereby reduced to a minimum. The advantage of employing a substantially vertical slit is believed to be due to the fact that the convection currents set up materials.

in such a slit facilitates the separation of the unlike fractions resulting from the thermal diffusion.

Among the more important variables influencing the method and apparatus of this invention are the length of the slit, the width orlateral dimension of the slit, the thickness of the slit, the temperature gradient, the average temperature of operation, the ratio of the rates of withdrawal of the top and bottom products, the slot dimensions, the flow rate of liquid through the slot, the composition of the liquid undergoing thermal diffusion, the position of the inlet slot with regard to the outlet slots, and the extent of desired liquid product separation.

The thickness of the slit is usually less than about A; of an inch. Slit thicknesses within-the range of 0.01 to 0.10 inch are generally employed. Too fine a slit results in too low a throughput for a given separation while too great a slit thickness, i..e., greater than about A; of an inch, ordinarily results in a greatly decreased degree of separation.

The extent of separation for a given slit thickness depends to a large extent upon the temperature gradient, i. e., the temperature differential between the hot and cold walls comprising the slit. The maximum temperature differential for a given slit thickness is related to the temperature of the hot surface which should not be so high as to cause turbulence due to ebullition, boiling, etc.; similarly, the cold surface must be above the temperature at which a solid phase would appear. Accordingly, there can be no definite upper limit to the temperature differential because the turbulence induced at a given temperature and the boiling point, as well as the appearance of a solid phase, vary with the nature of the liquid feed. There is no established lower limit to the temperature differential since a gradient of even 1 F. between the slit walls will effect a slow thermal diffusion. Under ordinary conditions of operation, a temperature differential of between about 50 C. and about 90 C. generally atfords good results.

The rate at which liquid feed can be charged into the slit depends upon the composition of the liquid, especially in regard to its difficulty of separation into unlike components, the temperature of operation, the temperature gradient, the slot dimensions, and the thickness, length, and width of the slit.

. The principal requirement in locating the inlet slot with regard to the outlet slots is that the liquid feed will notenter an outlet slot before being subjected to thermal diffusion. Generally, it is desirable to introduce the liquid feed through an inlet slot positioned intermediate two outlet slots and, if desired, the inlet slot may be positioned closer to one outlet slot than to another; and there may be any desired number of outlet slots.

The slot dimensions are defined by continuous slots across the lateral faces of the walls, either plane or curved, which define the slit. The lateral dimension of the slot desirably approximates the lateral dimension of the slit walls. With an unobstructed slot, i. e., a slot affording direct communication between the inlet or outlet tube and the slit, the vertical dimension or height of the slot is generally between about 0.01 inch and about 0.25 inch. With a slot formed of a porous structure,

i. e., having a porous structure intermediate the inlet or outlet tube and the slit, the slot area may be appreciably greater than in the case of the unobstructed slot; The vertical dimension or height of the slot formed of a porous material depends to a large extent on the porosity of such material. With less porous materials, the height of the slot may be greater than with the more porous Generally, the porosity of the structure employed will be between about 1 x 10- and about 5 x l0 inch average pore diameter, and with such materials the slot height will generally be in the approximate range of to /2 inch. It is to be understood that in every instance the actual dimensions of the slot are such that flow through the slot is uniform throughout its length.

This uniform, flow may be obtained from a backing header communicating with the 'slot. The dimensions of the backing header and slot are such that the pressure drop due toflow through the header is at least several times smaller than the pressure drop due to flow through the slot. At every elementary cross-section, the slot must offer substantially uniform resistance to flow. It is also to be understood that thermal disturbances in the region of the slot area are desirably minimized.

Any suitable means may be employed to maintain a temperature gradient across the slit. The walls forming the surfaces of the slit are desirably constructed of a solid heat-conducting material in order to maintain said surfaces at the desired temperatures. Conventional sources of heat, such as steam, electric devices, and hot circulating liquids, may be used to impart the desired temperature to the hot surface of the slit. Likewise, conventional cooling methods, such as liquid circulation, air-cooling, etc., may be employed to keep the temperature of the cooled surface at. the desired level.

The principal advantage of the method and apparatus of this invention is that continuous liquid separations of a different kind than achieved by other methods, such as distillation, adsorption, and solvent extraction, can be carried out on a commercially attractive scale with greater efficiency than heretofore attainable. This advantage is inherent in the method and apparatus of this invention since the necessity of carrying out separations by thermal diffusion on a small batch scale basis is avoided and continuous uniform lateral distributionof the liquid feed and finished product streams over the working surfaces of the thermal diffusion zone achieves an economy of heat and of apparatus not heretofore attainable.

It is to be understood that the above description is merely illustrative of preferred embodiments of the invention, of which many variations may be made within the scope of the following claims by those skilled in the art without departing from the spirit thereof.

We claim: 7

1. In a process for effecting continuous separation by thermal diffusion of a mixture having unlike components which are liquid under the conditions of separation wherein said mixture is continuously introduced into a substantially vertical slit formed of two smooth surfaces across which is maintained a temperature gradient and wherein a fraction containing a greater concentration of one of said unlike components than the initial mixture is continuously removed from one part of said slit and a fraction containing a greater concentration of another of said unlike components is continuously removed from another part of said slit, the improvement which comprises uniformly introducing said mixture through a porous feed inlet extending laterally across one of said surfaces to thereby achieve uniform lateral distribution of said mixture over the surface through which it is introduced into said slit and uniformly withdrawing said fractions through porous outlets, positioned above and below said feed inlet and extending laterally across at least one of said surfaces to thereby achieve uniform lateral withdrawal of the separated liquid fractions over the surfaces through which they are removed from said slit, the rate of liquid flow through each of the porous openings being uniform throughout the opening area thereof and further being characterized by being insufficient to induce turbulence in the liquid in said slit.

2. In an apparatus adapted for continuous liquid thermal diffusion made up of two substantially parallel vertical smooth walls spaced apart from one another to form a uniform narrow slit therebetween, means for providing a temperature gradient between said walls, withdrawal outlets communicating with said slit for removing separated liquid products therefrom at different levels and a feed inlet between said withdrawal outlets communicating with said slit for introducing unseparated liquid thereto, the improvement comprising, as a feed inlet, surfaces de- 9 fining a porous opening extending laterally across the surface of one of said walls and conforming substantially in lateral dimension thereto to thereby afford means for uniform lateral distribution of said unseparated liquid over the surface of the wall through which it enters said slit and, as withdrawal outlets, surfaces defining porous openings positioned above and below said feed inlet and extending laterally across the surface of one of said walls to thereby afford means for uniform lateral withdrawal of the separated liquid products from the surfaces of the walls through which they are removed from said slit.

3. In an apparatus adapted for continuous liquid thermal diffusion made up of two substantially parallel vertical smooth walls spaced apart from one another to form a uniform narrow slit therebetween, means for providing a temperature gradient between said walls, withdrawal outlets communicating with said slit for removing sep- I arated liquid products therefrom at different levels and a feed inlet between said withdrawal outlets communicating with said slit for introducing unseparated liquid thereto, the improvement comprising, as a feed inlet, a porous opening extending laterally across the surface of one of said walls and, as withdrawal outlets, porous openings positioned above and below said feed inlet and extending laterally across the surface of one of said walls, each of said porous openings conforming substantially in lateral dimension to the wall pierced thereby, having a porous structure of between about 1 X 10- and about 5 x 10- inch average pore diameter and being between about fie and about /2 inch in vertical dimension to attain uniform lateral distribution of unseparated liquid and uniform lateral withdrawal of resulting separated liquid products over the working surfaces of said slit.

References Cited in the file of this patent UNITED STATES PATENTS 1,716,934 Smith June 11, 1929 1,908,102 Arledter May 9, 1933 2,081,382 Piatt May 25, 1937 2,541,069 Jones et al Feb. 13, 1951 2,541,071 Jones et al Feb. 13, 1951 2,712,386 Jones et al. July 5, 1955 2,720,975 Jones et al. Oct. 18, 1955 2,720,976 Jones Oct. 18, 1955 2,720,978 Jones et al. Oct. 18, 1955 

1. IN A PROCESS FOR EFFECTING CONTINUOUS SEPARATION BY THERMAL DIFFUSION OF A MIXTURE HAVING UNLIKE COMPONENTS WHICH ARE LIQUID UNDER THE CONDITIONS OF SEPARATION WHEREIN SAID MIXTURE IS CONTINUOUSLY INTRODUCED INTO A SUBSTANTIALLY VERTICAL SLIT FORMED OF TWO SMOOTH SURFACES ACROSS WHICH IS MAINTAINED A TEMPERATURE GRADIENT AND WHEREIN A FRACTION CONTAINING A GREATER CONCENTRATION OF ONE OF SAID UNLIKE COMPONENTS THAN THE INITIAL MIXTURE IS CONTINUOUSLY REMOVED FROM ONE PART OF SAID SLIT AND A FRACTION CONTAINING A GREATER CONCENTRATION OF ANOTHER OF SAID 